[PATCH v5 2/2] irqchip/riscv-aplic: force synchronous probing

[Vladimir Kondratiev]

The APLIC driver leaves probe_type unset, so it follows
PROBE_DEFAULT_STRATEGY and is probed asynchronously when the command line
requests it (driver_async_probe=). The probe of an APLIC instance updates
state shared by all instances without any locking:

- the check-then-set of aplic_syscore_registered; two instances can both
  observe it as false and both call register_syscore(), inserting the same
  list node twice and tripping CHECK_DATA_CORRUPTION ("list_add double
  add") in __list_add_valid_or_report();
- the global aplics list, modified by aplic_pm_add()/aplic_pm_remove();
- aplic_direct_parent_irq, where more than one instance can pass the check
  and register its own CPU hotplug state;

Interrupt controllers are required early and have no benefit from
parallel probing, so rather than adding locks around each of them mark the
driver PROBE_FORCE_SYNCHRONOUS. Probes then run one after another from
driver registration, and deferred probe retries are serialized by the
single deferred probe work item, so the shared state is never accessed
concurrently. Probing is also blocked across suspend, so it cannot overlap
with the syscore callbacks either.

Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev at mobileye.com>
---
 drivers/irqchip/irq-riscv-aplic-main.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-riscv-aplic-main.c b/drivers/irqchip/irq-riscv-aplic-main.c
index 5369078f3d00..3c10dbf3b492 100644
--- a/drivers/irqchip/irq-riscv-aplic-main.c
+++ b/drivers/irqchip/irq-riscv-aplic-main.c
@@ -118,7 +118,8 @@ static struct syscore aplic_syscore = {
 
 /*
  * Not __ro_after_init: probe can be deferred (e.g. MSI mode waiting for the
- * IMSIC) and complete after the init memory is made read-only.
+ * IMSIC) and complete after the init memory is made read-only. Probing is
+ * synchronous (see aplic_driver), so no further serialization is needed.
  */
 static bool aplic_syscore_registered;
 
@@ -413,6 +414,12 @@ static struct platform_driver aplic_driver = {
 		.name		= "riscv-aplic",
 		.of_match_table	= aplic_match,
 		.acpi_match_table = ACPI_PTR(aplic_acpi_match),
+		/*
+		 * Probes of multiple APLIC instances share global state (the
+		 * syscore registration and the parent interrupt of the
+		 * direct mode) and must not run concurrently.
+		 */
+		.probe_type	= PROBE_FORCE_SYNCHRONOUS,
 	},
 	.probe = aplic_probe,
 };

-- 
2.43.0